1. Field of the Invention
The invention relates generally to the field of solids separation through the use of a gyratory sifter. More specifically, the invention relates to methods and systems for cleaning (“deblinding”) gyratory sifter screens.
2. Description of the Related Art
Gyratory sifters are used in a variety of applications for separating solids by size. These applications include separating particles of sugar, flour, sand and various chemical powders. Typical gyratory sifters include screens or perforated plates oriented generally horizontally, sloping from the head to the tail end of the sifter. FIG. 1 depicts a cross-section of one example of a gyratory sifter, shown generally at (1). Screens (10) are depicted in FIG. 1. Screens (10) are designed to allow particles with generally smaller diameters than the openings in the screen to pass through the screen, while larger particles remain above screens (10). Gyratory sifter (1) often uses an eccentric drive mechanism or other motive force (not shown) to provide a circular motion substantially in a horizontal plane, as shown in FIG. 2. Circular lines (100) depict the circular motion imparted on the particles on screens (10).
One problem often associated with the use of gyratory sifters is the tendency of the particles-to-be sifted to agglomerate or otherwise stick together. Further, these agglomerated particles-to-be sifted may plug the openings in the screens, preventing smaller size particles from properly passing through the screens. In addition, particles approximately the same size as the openings may plug the openings rather than pass through them, due to eccentricities in particle diameter.
Various means are known in the art to remedy the foregoing problems, including the use of roller brushes underneath the screens having bristles that project through the screen, and air jet cleaning which forces air through jets below the screen to dislodge particles that may be plugging holes in the screens. These cleaning methods may be undesirable, as they often require that the sifter operation be halted during the cleaning process and involve complicated additional machinery beyond what would normally be required for the sifter. Another method is the use of cleaning elements, typically spheres, to clean the screens during operation of the sifter. As depicted in FIGS. 1, 3 and 4, in using spheres for cleaning gyratory sifters, ballboxes (20) are located beneath screens (10) in gyratory sifter (1). Ballboxes (20) include ballbox screens (22). Ballbox screens (22) typically have significantly larger openings than the screens (10) and are configured to allow particles that pass through the screens (10) to freely pass through the holes in ballbox screen (22). Ballbox screens (22) are bounded by sides (24). Slats (26) are often included as part of ballbox (20) to provide support for ballbox screens (22). Ballbox (20) is configured to contain a plurality of deblinding spheres and to maintain those spheres between it and screen (10). In the sphere cleaning method, the spheres are configured to bounce between ballbox screens (22) and screens (10), dislodging any agglomerated or near-hole-sized particles that may have plugged the openings in the screens (10). The sphere method, compared to the roller brushes and air jet cleaning, is typically simpler and easier to maintain, and is typically used while the gyratory sifter is operating to separate particles. However, because the motion of the gyratory sifter is mostly in a nominally horizontal plane, i.e., a plane along the face of screens (10), little force in the nominally vertical plane, i.e., normal to the face of screens (10) may be imparted to the round spheres, limiting their effectiveness in dislodging the agglomerated or near-hole-sized particles on screens (10).
Accordingly, there exists a need for a cleaning method for a gyratory sifter that may provide more effective cleaning than methods known in the art.